Heschl gyrus and its included primary auditory cortex: structural MRI studies in healthy and diseased subjects

Despite the fact that the Heschl gyrus (HG) is a crucial brain structure as it contains the primary auditory cortex (PAC), relatively few structural MRI studies have concentrated upon it. We propose that this may be attributed in part to the considerable variability of this structure and, most importantly, to the lack of unified criteria for defining the extent of the PAC along the MRI-determined landmarks of the HG, which ultimately affects the reliability and reproducibility of these studies. This review highlights three aspects: first, the standard and variant anatomy of the HG and PAC with particular focus on MRI definition of these regions; second, the importance of studying the HG and PAC in health and disease using structural MRI; and, third, the problem of MRI localization of the PAC. The scientific community should be aware that the HG and its included PAC are not synonyms. Additionally, owing to the great complexity and variability of these regions, future MRI studies should be cautious when using single brain-based atlas or maps generated by simply averaging across individuals to localize these regions. Instead, and while waiting for future in vivo microstructural localization of the PAC, the use of probabilistic and functional maps is advantageous but not without shortcomings.